Photomasks are particularly useful in the manufacture of circuit patterns, such as, for use in the manufacture of integrated circuits in the electronic arts. Typically, a photomask comprises a patterned metal film such as chromium, nickel or aluminum in a thickness in the order of 1,000 A. deposited on a transparent base, such as glass or quartz. It is generally manufactured by depositing a thin film of the metal on the surface of the transparent substrate, coating the film of metal with a photoresist coating, exposing a patterned region on the photoresist coating, developing the photoresist coating, and removing the metal from the unprotected areas of the film by etching, leaving a patterned metal film on the substrate.
In the manufacture of metal photomasks, defects such as pin holes or missing portions of metal film may occur. These defects in turn cause defective integrated circuits or other devices produced from these masks. Since the manufacture of photomasks is generally a time consuming and relatively expensive operation, it is often desirable to correct a defective photomask rather than to discard it. One method for repairing a defective photomask has been described in U.S. Pat. No. 3,748,975. This method is similar to the method of manufacturing the original photomask in that it involves depositing a photoresist coating over the surface of the photomask and exposing the photoresist coating to light in the region overlying the defect to be corrected, developing the photoresist coating and then, depending upon the kind of photoresist coating used, the defect can be etched away where the defect is one consisting of a protrusion of excess metal or can be rendered opaque where the defect consists of holes or missing areas. When this method is employed for repairing pin hole defects or the like, one must use essentially all of the same steps employed in making the initial photomask. In the procedure of the present invention, fewer steps are required and materials other than photoresists can be employed when economically desirable.